This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-022656, filed Jan. 31, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a print board, and more particularly to a print board including a measuring wiring pattern for measuring a characteristic impedance of a measurement target signal wiring pattern.
In a print board used for an electronic circuit of an operational frequency of over 100 MHz, and particularly used for implementing an RF circuit for a wireless communication and Direct-RDRAM or the like of Rambus Co., it is important to control a characteristic impedance of a signal wiring pattern. For this reason, a measuring wiring pattern for measuring the characteristic impedance of the signal wiring pattern is provided.
This measuring wiring pattern is a linear pattern for measurement only and has a length of more than a predetermined length which is prescribed for a measurement of the characteristic impedance. (1) a width of the wiring pattern (copper), (2) a thickness of the wiring pattern, (3) a dielectric constant of an insulating layer, (4) a thickness of the insulating layer, and (5) a type of line (microstrip line structure or strip line structure) are usually considered as factors for deciding the characteristic impedance of the linear pattern.
Therefore, by coinciding a width of the measuring wiring pattern with that of a signal line of the measurement target signal wiring pattern, a characteristic impedance of the measurement target signal wiring pattern can be investigated from a result of the characteristic impedance of a measuring wiring pattern.
Nevertheless, in a practical print board, a thickness of the insulating layer in item (4) is often not uniform and the thickness of the insulating layer beneath the measurement target signal wiring pattern does not coincide with that of the insulating layer beneath the measuring wiring pattern. Since the insulating layer is formed on a patterning conductive layer (plain layer for a power source or a ground), the thickness of the insulating layer which is formed on the conductive layer changes subtly according to a patterning form of the conductive layer.
Therefore, as a coincidence of only a pattern width is used in a prior art, a subtle change of the pattern width affects the result of measurement, so it is difficult practically to measure the characteristic impedance correctly.
When the measuring wiring pattern is arranged on a periphery of the print board, a sacrificed portion of a print board outside the product or the like, a thickness of the insulating layer is different between beneath the measuring wiring pattern and beneath the measurement target signal wiring pattern. In the periphery or sacrificed portion, as the plain layer is beforehand scraped the side off in order not to expose outward, the insulating layer of that portion is usually made thinner than the inner side of the print board.
Accordingly, it is an object of the present invention to provide a print board in which it is possible to correctly measure a characteristic impedance of a measurement target signal wiring pattern with reducing the measuring error of a characteristic impedance based on a difference of a thickness of an insulating layer.
According to the present invention, a print board is formed by forming an insulating layer on a patterned conductive layer and forming a wiring pattern layer on the insulating layer. A measuring wiring pattern for measuring the characteristic impedance of a measurement target signal wiring pattern in the wiring pattern layer is provided on the wiring pattern layer, and the conductive layer is patterned so that a containing percent of a conductive material per unit area of the conductive layer become approximately the same in a forming area of the measurement target signal wiring pattern and in a forming area of the measuring wiring pattern.
In this print board, since the conductive layer is so patterned that a containing amount of the conductive material per unit area of the conductive layer becomes approximately the same between in the forming area of the measurement target signal wiring pattern and in the forming area of the measuring wiring pattern and the insulating layer is formed on the conductive layer, a thickness of the insulating layer in the measuring wiring pattern forming area can be coincided with a thickness of the insulating layer in an actual signal line (measurement target signal wiring pattern) forming area.
Therefore, a measuring error of the characteristic impedance due to a difference of a thickness of the insulating layer can be reduced, and using the measuring wiring pattern, the characteristic impedance of the measurement target signal wiring pattern can be correctly measured.
Further, in order to make a containing amount of the conductive material in the neighborhood of the forming area of the measuring wiring pattern the same as a containing amount of a conductive material in the neighborhood of the forming area of the measurement target signal wiring pattern, an arbitrary shaped or formed conductive material removal area is formed in a conductive layer in the neighborhood of a forming area of the measuring wiring pattern and a containing amount of a conductive material in the conductive layer is adjusted. For example, it is preferable that a via hole for a pseudo interlayer hole or a through hole may be arranged or a cutout portion may be formed.
When the measuring wiring pattern is formed on a periphery of the print board, a conductive material removal area is formed only on the inner side of the print board with regard to the measuring wiring pattern. Thereby, it is possible to reduce an area of a necessary conductive material removal area and a layout which is preferable to a high density packaging can be realized.
If a clearance diameter for an interlayer hole or a through hole formed in the conductive layer in the neighborhood of the forming area of the measurement target signal wiring pattern is set to the smaller value than a clearance diameter for an interlayer hole or a through hole formed in the conductive layer in the neighborhood of a forming area of other wiring pattern, a difference between a containing amount of the conductor material in the neighborhood of the forming area of the measurement target signal wiring pattern and a containing amount of the conductive material in the neighborhood of the forming area of the measuring wiring pattern may be small. This structure can be utilized individually, but may be used in combination with a structure provided with the conductive material removal area.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.
The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.